Northern silky oak
Cardwellia sublimis. Family: Proteaceae
Oak; bull oak; silky oak
- Large tree grows to 40m high.
- Stem grows to 2m diameter.
- Trunk, usually without buttresses, is normally straight.
- Bark is slightly flaky to non-descript.
- Outer blaze is commonly biscuit-brown.
- Distribution is limited to North Queensland between Mt Spec, near Townsville, and Bloomfield.
- Heartwood is pale pink to brown.
- Sapwood is usually almost white.
- Texture is moderately coarse and varies.
- Quarter-sawn timber best shows the decorative grain.
- Construction: used extensively, in the past, in North Queensland general house framing, cladding, lining, moulding, joinery (particularly windows) and flooring; now confined more to use in joinery.
- Decorative: plywood, furniture, outdoor furnishings, joinery, shop and office fittings, turnery, carving, inlay work.
- Others: used, in the past, for boat building (light), brushware, gunstocks, cooperage, vehicle and coach building.
- Density: 560kg/m3 at 12% moisture content; about 1.8m3 of seasoned sawn timber per tonne.
- Strength groups: S6 unseasoned, SD7 seasoned.
- Stress grades: F4, F5, F7, F8 (unseasoned); F5, F7, F8, F11 (seasoned) when visually stress-graded according to AS 2082—2000: Timber—Hardwood—Visually stress-graded for structural purposes.
- Joint groups: J4 unseasoned, JD4 seasoned.
- Shrinkage to 12% MC: 4.7% (tangential), 1.6% (radial).
- Unit shrinkage: 0.31% (tangential), 0.13% (radial)—these values apply to timber reconditioned after seasoning.
- Durability above-ground: Class 4 (life expectancy less than 7 years).
- Durability in-ground: Class 4 (life expectancy less than 5 years).
- Lyctine susceptibility: untreated sapwood susceptible to lyctid borer attack.
- Termite resistance: not resistant.
- Preservation: sapwood readily impregnates with preservative but the heartwood can’t be adequately treated using currently available commercial processes.
- Seasoning: satisfactorily dries using conventional air and kiln seasoning.
- Hardness: soft (rated 5 on a 6-class scale) to indent and work with hand tools.
- Machining: machines, and turns well, to a smooth surface.
- Fixing: no difficulty using standard fittings and fastenings.
- Gluing: satisfactorily bonds using standard procedures.
- Finishing: readily accepts paint, stain and polish; you may need to fill the open grain before polishing the timber.
- Sapwood: creamy white.
- Heartwood: pink to pinkish-brown..
- Texture: coarse and irregular, a broad ray figure (pattern) on quarter-sawn surfaces, straight grain.
- Growth rings: indistinct.
- Vessels: large, numerous, solitary or in short tangential hoops between the rays; no tyloses, but occasionally vessels are filled with whitish deposits or red-coloured gum.
- Parenchyma (soft tissue): abundant, aliform and confluent, including vessels between rays; forming loops, generally, concave outwards; an occasional short tangential apotracheal band.
- Rays: 2 distinct kinds are (a) broad to very broad, plainly visible without a lens on all surfaces, and (b) fine, indistinct even under hand lens.
- Burning splinter test: match-size splinter burns to charcoal.
- Splinter shape: fine needle-like splinters produced when cutting across the grain are characteristic of this species and can be used to separate northern silky oak from similar species.
Research and resources
- Boland, DJ, Brooker, MIH, Chippendale, GM, Hall, N, Hyland, BPM, Johnston, RD, Kleinig, DA and Turner, JD 2006, Forest trees of Australia, 5th edn, CSIRO Publishing, Collingwood Australia.
- Bootle, K 2005, Wood in Australia: Types, properties and uses, 2nd ed., McGraw-Hill, Sydney.
- Last reviewed: 12 Dec 2018
- Last updated: 12 Dec 2018